THE ABSORBENT SYSTEM. 93 
gastric secretion was acid, these are alkaline; and their 
office seems to be —the subdivision of the fatty matter 
into minute particles (emulsion), till they are diffused 
through the liquid, like atoms of butter in milk, thus fit- 
ting it to be absorbed into the blood; and the completion 
of the work begun by the saliva and gastric juice. In this 
they are assisted by the “intestinal juice” secreted by the 
mucous lining of the small intestine, the action of which 
is merely supplementary. The chyle is slowly driven 
through the small intestine by the creeping, peristaltic 
motion of its walls, the nutritious portion being taken up 
by the absorbents, as described in the next chapter, while 
the undigested part remaining is discharged from the large 
intestine. 
CHAPTER XI 
THE ABSORBENT SYSTEM. 
TueE nutritive matter (chyle), prepared by the digestive 
process, is still outside of the organism. How shall it 
enter the living tissue ? 
In animals, like the Infusoria and Polyps, whose digest- 
ive department is not separated from the body-cavity, the 
food, as soon as dissolved, mingles freely with the tissues 
and organs it has to nourish. In the higher Invertebrates 
having an alimentary canal, the chyle passes, by simple 
transudation, through the walls of the canal directly into 
the soft tissues, as in Insects, or is absorbed from the canal 
by veins in contact with it, as in Sea-urchins, Mollusks, 
Worms, and Crustaceans, and then distributed through the 
body. 
In Vertebrates only do we find a special absorbent sys- 
tem. Three sets of vessels are concerned in the general 
